The use of directional horizontal underground drilling has become increasingly effective and more widely accepted for the installation of water and gas pipes, underground utilities, telephone lines, and cables. Prior to the use of these horizontal drilling techniques, open trenches were generally required to place pipes, cables and wires underground. With such trenches, particular difficulties were encountered in crossing bodies of water, roads, driveways, improved areas, or existing underground utility installations. Accordingly, horizontal directional drilling techniques have allowed for the elimination of open trenches in many situations, particularly when encountering obstacles at or near the surface.
With the development of these horizontal drilling techniques, there has been an historic need to develop a more precise and cost effective system to effectively control the route of travel, depth of travel, and point of emergence for the drilling apparatus. In response to these needs, a drill radio-transmitting unit was developed and incorporated into the underground directional drilling apparatus to broadcast a remote signal to aid in identifying the direction of travel, depth of the drilling apparatus, orientation within the borehole of the drilling apparatus, and inclination of the drilling apparatus. The development of drill transmitting units, in turn, created a demand for resilient housing to contain and protect transmitting equipment which was located near the leading or cutting end of an underground directional drilling tool. Further, greater demand was created for more precise directional control of the boring operation.
When in use, the area of underground drilling is an extremely hostile environment. As such, a desirable underground directional drilling tool should be sufficiently durable to operate within this hostile environment over an extended period of use and an extended product life. Additionally, there remains a continuing need to improve the efficiency of the tool in stabilizing, positioning and controlling the drill bit in downhole operations. It is therefore an object of the present invention to provide a tool for use with directional drills, which tool is efficient in stabilizing, positioning and controlling the direction, depth, orientation and inclination of the drilling operation.
The applicant has previously developed and patented an improved underground directional drilling tool having an improved method for control. As discussed in the inventor""s U.S. Pat. No. 6,050,350, which is incorporated herein by reference, there has been and continues to be a need for durable, steerable underground drilling apparatus of simple construction. Simple construction is important to allow for ease of repair, reduction of downtime associated with repair, and minimization of repeated removal of the apparatus from the down hole work area in order to implement repairs. The ""350 patent describes an underground directional drilling tool wherein the drive shaft is offset from the centerline of a transmitter housing thus causing the rotation of the drill bit to cut an arcuate path. An overall travel path that is generally straight or that lies in a generally desired route may be formed through periodic rotation of the tool housing, thus changing the immediate arcuate path. As explained in the ""350 patent, this design includes a jaw clutch and simple engagement of the housing when the drill string is pulled back. When the housing is so engaged, it may be conveniently rotated through manipulation of the drill string. In this manner, the invention of the ""350 patent provides for a simple, reliable, and durable construction that eliminates the need for complex steering devices, motors, and controls. The invention of the ""350 patent therefore serves the objective not only of providing a resilient transmitter housing, but it provides a multi-purpose tool that effectively accomplished the objectives of simplicity, durability, and longevity that are important in the hostile, underground environment. The tool also provides a method for steering the tool. In order to pass the torque of the drill string through the tool housing to the drill bit, the ""350 housing incorporates a cylindrical bearing in each end of the housing and a cylindrical thrust bearing at the rear. In the ""350 housing, the cylindrical thrust bearing and cylindrical bearings carry rotational torque from the driveshaft to the transmitter housing. This creates significant wear on the bearings requiring frequent maintenance and replacement. Further, the rotational torque carried by these bearings to the tool housing creates instability in downhole use that makes directional control more difficult.
The present invention, generally referred to herein as the underground directional drilling tool, seeks to improve in these areas by maintaining simplicity in design, while eliminating the cylindrical bearings in each end of the housing and, further, eliminating the thrust bearing positioned at the rear of the housing. As with the invention of the ""350 patent, the housing is offset from the centerline of the drill bit. The new design represented by the present invention reduces the rotational torque transferred from the drive shaft to the offset transmitter housing. Effective use of subassembly bearings allows the drive shaft and rotational components of the subassemblies to operate independently of the direction-controlling, offset transmitter housing as the offset transmitter housing floats on the non-rotating outer sleeve of the subassemblies. It is therefore an object of the present invention to eliminate the bearings in each end of the offset transmitter housing and eliminate the cylindrical thrust bearing that pushes the offset transmitter housing by positioning bearings in the subassemblies located at each end of the housing. These subassemblies are threadably connected to each end of the drive shaft passing through the offset transmitter housing. The housing then floats on the non-rotating outer sleeve of each of the subassemblies independent from the rotating drive shaft.
The underground directional drilling tool includes-a rear subassembly and a front subassembly that allow an offset transmitter housing to float on the non-rotating outer sleeves of each of the subassemblies without the use of bearings in or on the housing. Rather, the subassemblies are composite elements. Rear radial bearings and radial thrust bearings are constrained between the rear inner core and the rear outer sleeve of the rear subassembly. This eliminates the cylindrical bearings and cylindrical thrust bearings that were subjected to high wear. Also, the rear subassembly accommodates the drill string and the drive shaft, and provides for the transmission of drilling fluid and torque there between while maintaining a non-rotating rear outer sleeve for advancing the housing as the drilling progresses. Since the rear outer sleeve does not rotate as it advances the offset transmitter housing, it does not transfer significant torque to the housing.
The front subassembly includes a front inner core having a jaw clutch, which core is adapted to couple the drive shaft and a drill bit. Forward radial bearings are constrained between the front inner core and a front outer sleeve to, again, provide a front subassembly with an outer sleeve that is rotationally independent of the drive shaft and that is able to engage and disengage the offset transmitter housing. In both subassemblies, the bearings are better sealed and longer wearing as compared to the use of thrust bearings or cylindrical bearings positioned directly upon the offset transmitter housing in the tool represented by the ""350 patent.
The offset transmitter housing has a seal affixed to the front and a seal affixed to the rear that slide over the exterior of the front and rear subassemblies to prevent drill cuttings and other debris from entering the tool. Longitudinal manipulation of the drill string may be used to engage and disengage the jaw clutch.